In a modern microwave communication system, band-pass filters (BPFs) are required to be provided with good selectivity, out-of-band rejection, wide stopband and small structure. Although traditional multi-mode BPFs based on loadable resonator are provided with good selectivity, there are many spurious passbands. However, on the other hand, a defected ground structure resonator (DGSR) is provided with many advantages. The tunability of the resonant mode of the filter in the existing art are poor.